1. Field of the Invention
The present invention relates to a method for compensating steering of a motor drive power steering system. More particularly, the present invention relates to a method for compensating steering of a motor drive power steering system, in which the motor drive power steering system determines a slip of a vehicle, calculates a steering compensation value, and controls a gain based on moment input from an electronic stability program system under coordinate control between the motor drive power steering system and the electronic stability program system, so that stability of the vehicle can be enhanced by reducing heterogeneous steering and preventing oversteer.
2. Description of the Related Art
In general, there are many cases where a power steering pump is used to allow a steering wheel to be easily turned in a vehicle steering system, and most power steering pumps employ a system for making easy left and right turns based on an oil flow obtained when an engine is driven to rotate.
For this purpose, a motor drive power steering (MDPS) system has recently been applied to some kinds of vehicles.
The MDPS system does not utilize the oil flow due to rotation of the engine, but utilizes a system that employs rotation of a motor to make a steering wheel easy to turn. The MDPS system has a prominent effect on improving fuel economy since it reduces engine load.
In the MDPS system, an MDPS unit is provided in the steering system to control the motor and output a steering-angle signal.
Further, an electronic stability program (ESP) system has recently been applied to some kinds of vehicles. The ESP system selectively applies a brake on front, rear, left and right wheels to prevent the vehicle from slipping due to an extremely unstable state when accelerating, braking or cornering, thereby not only stabilizing behavior of the vehicle but also correcting a driver's mistake. The ESP system includes an ESP unit.
As such, if the MDPS system and the ESP system are provided to the vehicle, a controller area network (CAN) communication is basically employed for data communication between these systems.
The above descriptions are related not to the prior art, but just a background of the invention.
In the case of coordinate control through the CAN communication between the MDPS system and the ESP system, the ESP system controls the MDPS system to have torque such that a driver feels heavy steering at oversteer or understeer, thereby inducing driver counter steer.
However, if the ESP system just applies certain torque to the MDPS system, there arises a problem in that the driver feels heterogeneous steering.
That is, the ESP system supplies overlay torque to the MDPS system by generating the counter-steering upon the excessive slip of the vehicle, so that the overlay torque is turned into the heterogeneous steering.
Further, the ESP system gives the MDPS system an overlay torque command without determining a detailed operation of the MDPS system, so that there is a limit to solve the heterogeneous steering.